Torque converters that can selectively lock-up are needed as consumers demand machines that operate at higher efficiency and higher performance. A lock-up torque converter may increase the efficiency and performance of a machine particularly at high operational speeds of the machine.
Typically, a lock-up torque converter has a lock-up plate. The plate is attached at one end portion to the turbine. At the other end of the plate, a friction-type lining, or a clutch system, is provided. The friction-type lining of the plate, or the clutch system, is selectively located in contact with the impeller cover of the torque converter to selectively lock the turbine to the impeller cover. In this manner, torque can be transferred directly from the engine to the turbine shaft and the torque converter function is bypassed.
There are various known methods to control a lock-up torque converter. In one known method, known as a two line method, fluid enters the torque converter between the power-take-off (PTO) shaft and the turbine shaft; fluid leaves the torque converter between the impeller and the stator. When the lock-up plate is engaged, this flow direction reverses.
The two line torque converter has the advantages of utilizing inexpensive parts and being inexpensive to manufacture. The two line torque converter suffers, however, from being difficult to cool down in certain designs and requiring a complex control system.
Open two line torque converters are also known. During hydrodynamic operation of these torque converters, fluid enters the torque converter between the stator and the impeller and between the impeller cover and the lock-up plate. Fluid leaves the torque converter between the stator and turbine. The lock-up plate can be used as described above with the two line torque converter.
Three line torque converters are also known. These torque converters can be disadvantageous as they are have more complex hardware than the two line systems but they can be more easily controlled.
Thus, it would be advantageous to have a two line system that utilizes the relatively simple hardware of the two line system, which is easy to control and which provides optimal function for the complete work range of the torque converter.